When it is required to unroll a strip of material wound onto a core in order to use the material, the core is fitted onto a spindle that is provided to rotate the core. The spindle must be equipped with a system that enables the spindle core to be fixed to the spindle so as to be rotatable with the spindle when it is required to unroll the strip of material. This will permit the rotary movement of the spindle to rotate the core. Further, in the field of photographic materials, operations requiring very high precision such as cutting or perforation are often done after unrolling. It is therefore necessary that the core is centered in relation to the axis of the spindle so that the strip of material is unrolled in a precise, regular and uniform manner.
Known systems are provided for rotatably fixing a core and a spindle to each other, which comprise pads, for example three in number and arranged at 120.degree., and provided to exert a pressure on the core.
FIG. 1 represents a first system wherein a chamber of air 10 is placed inside a spindle 11 and its axis is joined with the main axis of the spindle. The chamber of air 10 is provided to move pads 12. When it is required to rotatably fix the core 13 with the spindle 11, air is injected into the chamber of air 10 so that the chamber of air exerts a pressure on the pads. This pressure is a function of the air injected into the chamber. Such systems allow a fixed position of the core on the spindle to be obtained that does not assure centering of the core on the spindle. The chamber of air takes up a position of balance and exerts a pressure on the pads even though the core is not centered.
FIG. 2 represents a second type of system for making the core 20 and the spindle 21 rotatably fixed to each other. It also comprises three pads 22 that extend from the spindle 21. Each pad is fixed to a practically truncated cone moving part 23. A practically truncated cone part 24 is provided inside the spindle in a complementary way to the part 23 and is fixed. The part 23 can be moved thanks to a spring 25 making the part 23 and the spindle 21 fixed to each other at the larger base of the cone, approximately at the center of the base. The part 23 slides along part 24. The part 23 has a knob 230 at the larger base of the cone, at the periphery of the base. The part 23 is arranged in the spindle 21 in such a way that the knob 230 is opposite the pad 22, closest to the spindle axis. A pin 26 is mounted in the spindle according to the main axis of the spindle. The pin 26 is not fixed to the part 23. The pin 26 is arranged to slide according to the axis of the spindle when an external pressure is exerted on it. When the pressure exerted on the pin is enough, the pin comes to a stop against the knob 230 of the part 23, which causes the movement of each of the parts 23 with a pad. Each spring is then compressed and the practically truncated cone part 23 slides along the part 24. Each pad 22 moves in such a way that it no longer extends beyond the spindle, and a core can then be threaded onto the spindle. The problem encountered in this type of system is that centering the core on the spindle is very difficult. Each pad moves thanks to the presence of a spring, a spring being provided to move one pad independently from the other pads. The movement of each pad depends on the characteristics of each spring and thus varies easily from one pad to another. Thus the core is difficult to center in relation to the axis of the spindle.